Using Flash Beyond The Guide Number Distance.

On Feb 2, 1:39 pm, "Pat" wrote:
snip

Another option, but quite a bit more expensive, is to hide a few
flashed around the image to light up what you want. Your flash can be
used as a master to fire either dedicated to dumb slaves that are down
near your subject.

One combination I have used is a tripod and manual flash. With any
exposure longer than the flash recycle time, you can fire the flash
twice. With even longer exposures, you can fire the flash many
times. Keep in mind that you have to fire the flash (at full power)
four times to double the distance. I've even been known (in my
younger days) to run to a new location while the flash was recycling.

The technique works OK, (not really well) because noise still
accumulates with the long exposure.

Austin

Mardon wrote:
At 105mm & ISO100 my Canon Speedlite 580EX has a guide number of 58
(meters). At ISO3200 (maximum ISO of the Canon 20D) the 'effective' guide
number becomes 328. My lens has a maximum aperture of f/2.8. This
indicates that in darkness, the maximum distance from the flash, at ISO3200
and f/2.8, is 117 meters for a 'properly' exposed photo. My question is
how far beyond this distance is a flash useful at night? The other night I
photographed a piece of snow removal equipment at 200 meters, f/2.8,
ISO3200, but it was badly underexposed. Even though the equipment was
still well beyond the guide number distance of my 580EX, would the use of
my flash have helped?.

Related question for the 'oldies'. I seem to recall that the large
flashbulbs I used back in the '60s really packed a wallop. I can't recall
the guide numbers of those things. Does anyone know? I suspect they were
well over 100 at ISO100 (expressed in the equivalent ASA in those days,of
course.)


Tripod, beanbag, or use self-timer to trip shutter with least camera shake.

Morton